Knowledge of the development of transepithelial transport in the intestine and colon of the fetal and neonatal animal is very limited, yet very important in understanding nutrition and fluid and electrolyte conservation of the fetal and newborn animal. The goals of this project are to observe the presence and changes in transport of NaC1 glucose, amino acids and water with development and to localize their site of transport. For example, it is anticipated that active transport of glucose in the fetal colon will be demonstrated, and that it will be shown to slowly disappear in the first few days after birth. The effects of corticosteroid hormones, mineralocorticoids and of other pharmacologic agents known to affect transport in the adult gut will be determined when possible by application to the maternal system and to the tissue in vitro. A new system for the microperfusion of the minute tissues of the fetal rat gut will be applied and when available, tissue from human infant gut obtained at the time of surgery for clinical indications will be studied using standard methods and Ussing chambers. Experiments in fetal rats will be carried from 3 days before birth up until the time of weaning at about 21 days. In addition to transport experiments dealing with nutrients, the permeability of the gut to a series of small molecules (PEG average molecule weight 400) will be made and compared with location in the gut and stage in development.